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Redoing front forks, what weight oil (big guy)

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15K views 30 replies 6 participants last post by  Obo  
#1 ·
Ok, I was going to wait till winter to do this however, I've got everything else going good / smooth on the bike and have a set of wheel bearings for the front wheel so I've decided to do the front forks before this weekend as well.

Now with it being said, I'm a big guy, 280lbs, If I'm under heavy braking from 70mph the front forks collapse... ALOT lol
Can't afford new springs so what size spacer / weight oil would you guys reccomend?
Thanks!
 
#3 ·
Manual calls for SAE 10W or 10W-20 for a 150 lb rider. As I understand it, SAE 10W motor oil has about the same viscosity as 2.5 wt or 5 wt fork oil. Here's a chart showing SAE motor oil viscosities:

SAE viscosity grades ? viscosity table and viscosity chart

From that it looks like SAE 10W has a viscosity of 4.1 at 100 degrees C, and 20W would be 5.6.

Here's a chart showing fork oil viscosities:

Fork oil weights

As you can see there is quite a bit of variation in fork oil viscosity even among oils that are supposed to be the same weight. Looks to me like 2.5 - 5 wt fork oils have viscosities of 4.1 - 5.6 @ 100 degrees C so I suppose that's what they recommend for 150 lb riders.

Incidentally, I changed mine over the winter before I looked all this up. I read that the manual specified SAE 10W and didn't realize that fork oils seem to be different. I used 7.5 wt Silkolene ProRSF which is like most 10 wt fork oil. I weigh 170 lbs and after the change I thought the front end was a bit too stiff. Now I understand why! I am waiting for warmer weather which should thin the fork oil a bit and I hope make the bike ride more smoothly before I decide whether to change it or not. We'll see.

Also, I suppose you could loosen the fork caps with an impact gun once forks are removed but why? It's very easy to break them loose on the bike. Just remember to loosen the top fork clamp bolt first. DAMHIK!
 
#5 ·
I agree with Lpscruggs, use a dedicated fork oil, single viscosity.

The stock oil is 10w. To make the forks stiffer you can up the oil weight (15 or 20), however any increase in oil weight and preload (with the adjustable caps or the pvc spacer mod) will effect how it handles the daily bumps as much as it does the braking dive. Making it so it doesn't dive would mean it handles daily bumps like a frozen pig.

I'd not recommend cap removal with an impact gun. You can easily strip the aluminum caps that way. Just clean any dirt from them and make sure you loosen the top triple clamp pinch bolts BEFORE you try and remove the caps. Keep the bottom triple tree bolts in. If you don't loosen / remove the upper clamp bolt you'll never get the cap off. After the caps are loose, loosen/remove the bottom triple tree bolts and slide the fork down and out.

I did my forks last year (replaced the fluid and added in 3/4" spacers (as I recall)) and it made a big difference. If you go with the adjustable preload caps (either ones listed in the forum or ones from an older 1000 Concours) you won't need to put in the plastic preload spacer.

Increasing the pressure in the forks through spacer and oil alone could result in the seals leaking if you don't do the spring as well. It's the spring that handles the "bump" and the fluid that handles the rebound.
 
#6 ·
You do have a copy of the service manual correct?
 
#11 ·
It's common for it to lock. Nothing to do with the fluids though. I just used a rubber mallet and gently tapped on the lower lip (where the seals are) while holding the upper tube in my hand and voila, it came free. It doesn't take much force to free it & it's fine to do it without oil in it.
 
#9 ·
FWIW... I ran the PVC mod with 10w Torco fork oil at 250lb plus gear and got good results for three years. My spacer was a hair over one inch. I tried 1.25 inch but couldn't get the caps on, so I trimmed it down slightly.

Guess what? You just have to pull really hard; one of the bushings got locked up. It happened to me too and it just took a little time. Don't do anything you'll regret... walk away from it a little while, come back, pull on it, and it will break free.
 
#12 · (Edited)
I have used a 7/8" spacers and Red Line brand Light weight 5wt oil. Very good oil, synthetic and very stable in it's performance. I highly recommend getting Kevin Cameron's fantastic book "Sportbike Performance Handbook. He is of Cycle World magazines writing staff (Top Dead Center) and one of the most notable authorities on motorcycle performance. This book has one of the very best sections on motorcycle suspension setup.
 
#13 ·
I remembered to dig thru my old files and found copies of the "how to's" on the old zr7.com site.

If anyone wants the word documents emailed to them just pm me with your email address.

Write up #1:

Contributed by Philip Darnall
I disliked the soft springs in the front forks of my ZR-7. Nobody made a replacement spring for the ZR-7 that I could find. So I went ahead and perform surgery on the forks and made my own parts.

I took a 2" long PVC Schedule 40 end-to-end connector and cut it into half. This gave me two 1" spacers for each fork. I removed the fork caps with a socket wrench. (Make sure that you have backed off the pinch bolts or the caps will never come off!) Once the caps were off, I pulled out the factory metal spacer. It is about 6" long and made of thin steel. I wanted to get a look at the spring and other goodies in the fork, so I needed to fish out more parts.

I made a simple hook out of a handy coat hanger. Reaching down into the fork about 8" I pulled up the spring. The factory setup had a real nice metal washer/spacer that sat between the spring and the main spacer tube. I took the spacer/washer off and let the spring fall back down into the stanchion tube. The spring had a nice lip on the top edge where the metal washer/spacer sat. So I dropped the PVC spacer into the fork.

I took my hook and made sure my custom spacer was fully seated on the spring. Next I dropped the factory washer/spacer on top of the PVC spacer. Then in went the original 6" metal spacer. I tried to put the caps back on.

Their was no way that I could compress the spring enough to screw the cap back on. I pulled the PVC spacer out and cut it down by 1/4" and put everything back together. This time the cap went on with a minimum of cussing!

I repeated the same steps for the other side.

Oh what a difference a small spacer makes. My ZR-7 sits up much higher now with the extra preload. When I sat on the bike (post modification) the fork sagged down about 3/4" at the most. The old setup would drop down about 2"! I could slam on the brakes and the front wouldn't dive near as bad as the original setup.

With the bike riding higher and diving less I could last longer on the ride home. My hands didn't go numb in the first ten minutes.

Total cost for the modification was under one dollar.


-----------------------------------------------------------------------------

Write up #2 :

PVC Fork Modification Kawasaki ZR-7S
Contributed by Josh Leonard (aka Qheuie)
The pictures here were taken when I was replacing the original inserts I had made (1 3/4") with shorter ones (1")
(just pictures of the left fork leg)
The diameter of PVC coupler to use is 3/4". The coupler is 2" long so you will have to cut it down.
Make sure you debur the plastic after you cut it. You probably don't want plastic flakes floating around in your fork.



Here I took the bars off.. simple enough. Then I loosened the clamp pinch bolts by the caps, make sure you do this or turning the fork caps out will be a pain.
I also took the bolts that hold the cable guides to the fork off so I could move the bars out of the way.
(an old pair of jeans worked great to catch spills and protect the paint)



This is how much the spacers stuck out when I opened the fork (there is a 1 3/4" spacer in already,
sorry for the dark image :)



This is what the stack of spacer(s) and washer looked like before I put it back in. Notice the order of insertion.
I made sure to put the "factory" (non-cut) side of the PVC down to meet the spring, the washer meets the cut side then.
(the washer is between the PVC and the metal.)



This is the stack sticking out just before I capped it with a 1" spacer (1 3/4" was too stiff for me)
Notice the difference in material hanging out (about 3/4", ha)



This is where the fun began. When I put in a 1 3/4" spacer, I had to have my roommate help me push and turn the cap in.
The 1" spacer was manageable by just myself.
Tip: thread the cap on without the factory spacer in just to find where it "catches" the threads in the fork. That way you can make a good guess as to where to start turning the cap when compressing the stack. (Did that make sense??) Make sure you don't cross thread the cap/fork tube! You can feel when the cap starts to thread, if it turns easy you are ok. If not, try again until it turns in easy

I repeated this procedure for the right fork leg and then put it all back together and torqued the bolts with my spanky new Craftsman torque wrench :)

I thought this was a neat, cheap upgrade. For the money it seems to help reduce sag quite a bit. I didn't like the feel of the 1 3/4" spacer so I went to a 1" spacer. I think 1" is going to be too soft, so I may go to a 1 3/8" spacer next. Also, I used the tool kit that came with the bike (yucky). If you have a 22mm 6 point socket or wrench, I would recommend using it on the caps.
 
#14 ·
Here's what my couplers looked like before I cut them:

 
#15 ·
I also made a DIY fork oil tool to set the correct height.

Based on the "real tool"




Syringe, plastic fish airline tubing, spare bathroom sink supply line and a rubber bushing.
 
#16 ·
Also I'm thinking of turning the clock back and installing Schrader air valves in the fork caps like my 1980 KZ750 E1 had. Back then I also installed a balance tube so I could pressurize both fork tubes equally easily. Air is a compressible spring. I used it to fine tune my front end depending on my intensions and the conditions.
 
#17 ·
Is there clearance with the bars do that without bar risers? I assume you are going to thread and fit the valves in a set of end caps.
 
#18 ·
Thanks again guys!
Just curious, why do they say to place the spacer above the spring / below the washer? wouldn't it be better above the washer / below factory spacer? or even on top of factory spacer?
Its going to have the same amount of pressure on it no matter its placement but I'd think there would be some movement with it contacting the spring / wear?
Thanks!
 
#20 ·
From what I recall the large spacer is very thin walled. Placing the plastic insert between the spring and the washer keeps it from possibly twisting / moving and damaging the spacer. The spring is relatively thick and combined with the surface area of the washer allows for a larger contact area than the spacer alone. It also prevents the chance the insert could break. It also allows the cut end of the insert to sit against the washer and the factory end of the insert to sit against the spring.
 
#21 ·
It will dive a bit less and feel different in the bumps. What you've done is compressed the springs a bit more. It won't have much effect on the rebound though. It's a good trick but in the end you've taken a bit of available play out of the forks - mind you the only way to properly fix this is with new specialty springs, but not having the $$ is part of why we do this cheap upgrade.
 
#22 ·
I'm using thick walled stainless steel tubing the same size as the spring and a washer above and below it. I've decided to order preload adjustment caps from the older Concours 1000. I'm going to buy them thru Bike Bandit. Or any suggestions who else to get them thru ?
 
#23 ·
How do they compare to the aftermarket ones price wise?
 
#24 ·
Oh, and here's a tidbit I found in my records as well, relating to the caps:

The GTR1000 (ZG1000 A9 to A16) - Concours for US models - from '94 onward has just the preload adjustment. Part numbers and costs per fork are as follows:

11012-1885, cap
92055-1050, O-ring

1994 ZG1000-A9 Concours FRONT FORK (ZG1000-A9)
1995 ZG1000-A10 Concours FRONT FORK (ZG1000-A10~A13)
1996 ZG1000-A11 CANADA ONLY FRONT FORK (ZG1000-A10~A13)
1997 ZG1000-A12 Concours FRONT FORK (ZG1000-A10~A13)
1998 ZG1000-A13 Concours FRONT FORK (ZG1000-A10~A13)
1999 ZG1000-A14 Concours FRONT FORK (ZG1000-A14)
2000 ZG1000-A15 Concours FRONT FORK
2001 ZG1000-A16 Concours FRONT FORK
2002 ZG1000-A17 Concours FRONT FORK
2003 ZG1000-A18 Concours FRONT FORK
2004 ZG1000-A19 Concours FRONT FORK
2005 ZG1000-A20 Concours FRONT FORK
2006 ZG1000A6F Concours FRONT FORK

Jenny e-mailed me an install guide for the fork caps:

[I stumbled on to some excellent articles about setting up your bikes' suspension at http://members.ozemail.com.au/~kenru...torcyclist.htm and /racemoto.htm. An edited version is attached at the bottom of this article. The articles indicate that sag should be set between 1/4 total travel for fast riding and/or smooth roads to 1/3 total travel for normal riding. According to the ZR-7 specifications, the wheel travel for both front and rear is 130mm (I have not verified this yet), which I calculate would require approximately 33 to 43mm (1ÂĽ to 1 Âľ inches) of sag.

The articles at www.zr-7.com on installing PVC spacers are OK. Philip Darnell started with 1” then settled on ¾”spacers which he said gave him a sag of ¾”. Josh Leonard started with 1 ¾” (!!) then settled on 1”. Based on the above, these would be set-up for sporty riding on smooth roads. However, neither of these guys have indicated what load the bike was carrying for the set-ups they used. Regardless of this, the only way they can adjust the sag now (for a change in load and/or riding comnditions) is to change the spacer.

Instead of using a fixed spacer, I have replaced the stock 41mm fork top caps with ones which have preload adjustment. This means I can easily change the front preload to suit the load and/or the riding conditions. Originally I looked at getting fork caps from a 1994 to 2002 Kawasaki GTR1000 (ZG1000 Concourse), but finding one at the wreckers with stuffed forks is impossible (they won't separate parts from a good fork) and I was quoted $125 AUD new. So I ended up buying a set of second-hand '95 ZX6R fork caps complete with preload and damping adjusters for $50 AUD.

On these particular fork caps, with the preload fully wound out, the part that goes into the stanchion is 42mm in length. The adjuster will compress the spring a further 16mm when fully wound in.The stock ZR-7 caps have a set preload of 13mm, which Kawasaki says suits the average rider of 68kgs when all the other settings are as per the owner’s manual. I weigh about 66kgs, so the stock settings suit me OK for normal riding. I removed the stock spacer, which is 220mm long, and replaced it with a shorter spacer and washer totalling 191mm in length. This has the bike at the same amount of preload as the OEM set-up with the adjuster fully wound out. (Note the top of the adjuster with it fully wound out just clears the bottom of the stock bars.) So, with the preload fully wound out, the only difference between the stock set-up and mine is that the air volume of the forks has now been reduced due to the area taken up by preload part. I assume this would have an effect similar to having raised the fork oil level and in theory should prevent it from diving so far under hard braking. I confirmed this on my test ride.

If you read the information on suspension set-up at that web address I e-mailed you a while back then you would see that for best results you should adjust the preload so that the bike uses about 1/3 of the total suspension travel when carrying it's normal load (i.e. you or you and pillion, etc).


Cheers,
Jenny.']


I'm back

Hi there

The Aussies can finally get onto this forum again!

Jarel was kind enough to forward on my e-mails regards the fork caps. The caps I got are from a 1995 ZX6R. If you look at the schematics at buykawasaki.com for '95 to '97 ZX6R's (ZX600-F1 to F3) the part numbers are 11012-1937 for the cap and 92055-1321 for the O-ring.

Yes, you can use an ordinary washer like I did instead of paying $10 for the OEM part.

I am so impressed with the result that I'm not going to bother installing the progressive springs.

Cheers,
Jenny
 
#26 ·
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#29 ·
Not cool. I'm cheap. (and almost everything I have to have shipped takes 6-8 weeks to get to me) lol
 
#31 ·
We're around $6/gallon (there's variables there for conversion of L to G and currency,) 15% tax on most other purchases (not on most grocery food items) & most transport companies (from couriers to airlines) also add on a fuel surcharge (the % varies) Most things here, not including taxes etc, are still about 1.5 to 2 times the price in the US and sometimes way more than that. Same items. Even if they are Canadian made. *shrugs*

On the plus side we have basically free healthcare (but not free pharmacare.)

I'm not fortunate enough to have enough disposable income to buy whatever I want. My dollars are hard earned and I have to scrimp and save for everything I have & want. Now I certainly have bought expensive things I wanted, but there has to be a very good reasons for it. It's always a trade off. I'm more ant than grasshopper :)